1. Field of the Invention
This invention relates to audio outputs in handheld devices. In particular, the invention relates to the handling of simultaneous audio outputs.
2. Prior Art
Over the years, many electronic devices have been sufficiently reduced in size to become portable, and in turn, small enough to be held and operated in the hand of the user. The advent of integrated circuits greatly increased the number of devices that could achieve portability and handheld status, as well as increasing the functionality of such devices.
Initially, handheld devices such as pagers, telephones and radios were single purpose devices that had a single audio source and a single audio output. For such devices, there was no contention or confusion between multiple audio sources.
As handheld devices became more sophisticated, they began to have multiple audio sources. Audio sources can be divided into two classes: signal events and continuous sources. In previous devices with multiple audio sources, the sources were usually either signal events (e.g. ringers or alarms), or continuous sources (e.g. speech or music), but not both. The audio output of such devices with multiple sources was obtained by prioritizing the inputs and selecting among them, or not prioritizing the inputs and simply combining them.
For purposes of this disclosure, prioritizing of audio sources is defined as establishing a ranking of relative importance between audio sources. Balancing of an audio output is defined as establishing a predetermined relative level between at least two audio sources that are present in an audio output.
Although telephones utilize both transient and continuous sources, they are typically mutually exclusive in use. For a service such as call waiting, a signal event may be introduced to the audio output of the receiving party's device by superimposing it on the conversation that prompted the call waiting signal, or by blanking the conversation. This is an example of simple mixing of two sources. Simple mixing is tolerable in telephones since the signal event duration is short and any loss of conversation can usually be recovered by an inquiry to the other party in the conversation that was interrupted. However, when a signal event is simply mixed with a source such as a radio broadcast, information lost through the interruption is usually not recoverable.
As the functional capabilities of handheld devices has increased, the number of audio sources that may be incorporated in a single device has expanded. The development of low cost memory and efficient compression algorithms has lead to a new generation of devices that are capable of providing both entertainment and communications functions. An example of such a device is a telephone that is capable of playing MP3 files.
The number of available audio sources in handheld devices has increased the probability that two sources may interfere. For example, a telephone having a stored music playback capability may ring while the music is playing. Typically, in the case of simultaneous signal event and continuous source combinations, the solution has been either to mix the sources or temporarily suppress the continuous source. Mixing of the two sources can render the information contained in one or both sources unintelligible. For example, if a music program is too loud, a signal event such as a phone ring or low battery alarm may not be heard. The suppression of one source results in the information from that source being lost during the period of suppression.
The combination of two continuous sources in a handheld device is usually dealt with by selecting one or the other, as in a radio/tape player. This is an example of prioritizing the inputs and producing a single output. However, there are situations when it would be desirable to combine two continuous sources and prioritize them with respect to the combined output.
For example, a device combining a wireless baby monitor and an FM band radio would have two continuous audio sources. The baby monitor signal could be received at the 2.4 GHz ISM band, and the radio signal at the commercial FM band. As a normal condition, the two sources would be combined so that the net effect is that of being in a single room with a baby and a radio. However, it would be desirable to intelligently control the relative sound levels to guarantee that the baby could be heard when crying, regardless of how loud the radio program was playing.